Alternating-current motor.



No. 745,957. PATENTED DEC. 1, 1903.

A.-GHURCHWARD.

ALTERNATING CURRENT MOTOR.

APPLIUATION FILED APR. 27, 1903.

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Witne sses. IhVenCor. j/ lexanderchurchward Patented December 1, 1903.

PATENT OFFICE.

ALEXANDER OHURCHWARD, OF NEW YORK, N. Y.

ALTERNATlNG-CURRENT MOTOR.

SPECIFICATION forming part of Letters Patent No. 745,957, dated December1, 1903.

Original application filed March 29, 1897, Serial No. 629,853. Dividedand this application filed April 2'7, 1903. Serial No. 154,377. (Nomodel.)

T0 at whom it may concern:

Be it known that I, ALEXANDER CHURCH- WARD, a citizen of the UnitedStates, residing at New York, in the county of New York and State of NewYork, have invented certain new and useful Improvements inAlternating-Current Motors, of which the following is a specification.

My invention relates to alternating-current motors of the type in whichthe armature has any usual direct or continuous current-winding andcommutator and is fed with singlephase alternating currents. Suchmachines, as is Well known, will start and develop power, but areordinarily inefficient and do not possess sulficient starting torque.When the motor is starting and running at low speeds, there are in thearmature eddy-current losses, self-induction, and losses due tohysteresis, which all tend to reduce the useful voltage by increasingthe self-induction in the motorcircuit. Consequently sufficient currentmay not pass to give a good starting torque. The usual method ofovercoming this difficulty is to use a motor which is unnecessarilylarge for the service required of it when running at speed or else toconstruct it so as to have an abnormally small self-induction in orderto allow sufficient current to pass at starting to give large torque, inwhich case it is inefficient when running at speed.

My presentinventiou consists, essentially, in a novel way of startingthis class of motors by adjusting the commutator devices during thestarting operation to position where the machine will oppose a lessself-induction to the alternating currents, thereby permitting astronger current to pass, and after the armature has attained speedadjusting the said commutating devices back to their norm-a1 position.

My invention is especially useful in connection with alternating-currentmotors Whose armature, having a direct or continuous current-winding andcommutator therefor for starting purposes, is operated in series with afield-coil, the alternating current being fed to the machine in such waythat when the armature revolves at synchronous speed the currents flowas continuous currents in the armature, being rectified by thecommutator used in starting, as desired, while they flow in the field asan alternating current to rapidly reverse the polarity thereof and toproduce in effect a rotary magnetic field.

In carrying out the invention the commutator-adjustment may be made byhand or by means of devices responsive to differences in speed of themachine-as, for instance, by any centrifugal governor connected to thecommutator-brushes.

In an application filed by me March 29, 1897, Serial No. 629,853, I haveillustrated and described an apparatus by which my invention can becarried out and have therein claimed the said apparatus. In the presentapplication, which is filed as a division of the aforesaid application,I shall claim the method employed in carrying my invention into efiect.

In the accompanying drawings, Figures 1 and 2,the two positions of thebrushes are illustrated diagrammatically in connection with a four-polemachine, and Fig. 3 illustrates the application of a centrifugalgovernor to moving the brushes.

The armature A is wound with any desired system of coils, such as isemployed on continuous or direct current dynamos or motors, butpreferably with what is known as the closed-circuit, winding, thecommutatorcylinder for which is indicated at a and thecommutator-brushes at Z). The latter are preferably mounted on anydesired construc tion of rocker, by which they may be adjustedcircumferentially around the cylinder, and are insulated from oneanother, as usual in the art. The machine is supposed to have in thisinstance four field-magnets 0, whose coils are preferably in seriescircuit with the armature. Alternating currents are fed to the machinefrom any desired source, as from a transformer, (diagrammaticallyindicated at D,) which by preference is adapted to supply a constantcurrent. These currents in the starting operation fiow in the armatureand field as alternating currents; but when the machine attainssynchronous speed they flow as continuous currents in the armature, butstill as alternating currents in the field.

In the starting operation the self-induction of the machine is high, andinsufficient current will pass to give a high starting torque.

To obviate this, I start the machine with the brushes set as in Fig. 1,in which they are shown slightly shifted from their normal positions, asshown in Fig. 2. This shifting of the brushes from their normal positionhas the effect of changing the relations of the poles of thefield-magnets and armature, and thus decreasing the mutual magneticreaction in the motor. This of course has the effect of reducing theself-induction of the motor. Other things being equal, of course thereduction of the magnetic reaction between the armature and the fieldsby shifting the brushes would have the effect of reducing the motortorque-as, for instance, in a direct-current motor-but since the motorunder consideration is an alternating-current motor the reduction of theself-induction by the reduction of the magnetic reaction of the armatureand fields is very great, so that the alternating current permitted toflow by such reduction is so far in excess of that which would flow werethe magnetic reaction between the poles and armature allowed to remainnormal that the increase in the torque resulting from this largercurrent far exceeds the slight decrease that would result under otherconditions. Consequently the torque of the motor is greatly increased atstarting by the slight shifting of the brushes, as shown in Fig. 1. Whenthe machine reaches the synchronous speed, the self-induction is greatlylessened, as the current then flows as a continuous current in thearmature. When the machine has reached the synchronous speed or as itruns up to such speed, the brushes are turned to theirnormal positionfor synchronous running, as indicated in Fig. 2. The adjustment may bemade by hand or automatically. The latter manner of adjustment isindicated in Fig. 3, whereI showacentrifugal governor G, connected tothe rocker carrying the brushes. When the machine is at rest, thegovernor holds the brushes in the position shown in Fig. 1, butisadjusted to hold them in the position shown in Fig. 2 when turning atthe synchronous speed. It is obvious that the invention may be used, ifdesired, in connection with any desired means for keeping or maintainingthe machine at synchronous speed. The centrifugal governor is connectedwith the armature in any desired way, so as to revolve at the same speedas the armature.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is-

1. The herein-described method of starting single-phasealternating-current motors having when operated at speed a continuous ordirect current armature system and commutator therefor, consisting infeeding alternating currents to said commutator and armature, with thecommutating devices adjusted to a position to give low self-induction inthe armature-circuit under the action of the alternating currents at lowspeeds, and after the machine has attained running speed, adjusting thesaid devices to normal position.

2. In a series-wound alternating-current motor having a continuous ordirect current armature and commutator, the hereindescribed method ofreducing the self-induction of the motor and obtaining increased torqueat starting, consisting in starting the machine with the commutatoradjusted away from normal position, as and for the purpose described.

3. The herein-described method of starting a single-phasealternating-current motor having a continuous or direct current armatureand commutator, which consists in reducing the magnetic reaction betweenthe armature and the field at starting.

4. The herein-described method of operating a single-phasealternating-current motor having a continuous or direct current armatureand commutator, which consists in reducing the magnetic reaction betweenthe fields and armature at starting and then increasing such reactionafter the machine has attained substantially running speed.

In witness whereof I have hereunto set my hand this 15th day of April,1903.

ALEXANDER OHUROl-IVVARD.

Witnesses:

L. C. Foss, O. D. REED.

